1. Field of the Invention
This invention concerns a digital filter in which samples are weighted by addressing a memory.
2. Description of the Prior Art
A memory has already been used, in the prior art of digital filters as a means to simplify or even eliminate multiplication operations. The digital filters in that case consist mainly of shift or delay operators, add or subtract operators and multiply operators using a read-only memory. In an article appearing in the American Review: IEEE Transactions, Vol. ASSP-22, No. 6, December 1974, and entitled "A new hardware realization of digital filters", Abraham PELED and Bede LIU present a new approach for the design of digital filters making use of recent advances in the technology of semiconductors and especially of programmable read-only memories. As it will be seen below, the solution proposed by the authors for the design of a second-order filter cell simplifies the arithmetic operation but requires the storage of 2.sup.5 values. But, since one of the advantages of digital filtering is the possibility, on the one hand, of modifying the basic cell while changing only the coefficients and, on the other hand, of designing filters of an order higher than two by several runs of the samples to be filtered in the same basic cell but with different coefficients, it is obvious that the required storage volume increases very rapidly.